Container system for the transport and storage of highly reactive materials

ABSTRACT

The invention relates to a container system for the transport and storage of highly reactive materials, which comprises an outer container ( 1 ) that encompasses at least one inner container ( 2 ) in which the radioactive material is disposed. The inner container ( 2 ) is resiliently received in the inner container so as to absorb shocks. The outer container ( 1 ) comprises a cylinder ( 4 ) whose jacket ( 5 ) consists of prestressed reinforced concrete molded by centrifugal action and is provided with a lid ( 6 ) and a bottom pate ( 7 ) that consist of reinforced concrete. Like the outer container ( 1 ), an intermediate container may consist of prestressed reinforced concrete molded by centrifugal action and may encompass the inner container ( 2 ). Preferably, the concrete parts of the outer container ( 1 ) and the intermediate container ( 3 ) are provided with, e.g., boroxyde as an additional neutron absorber. The resilient mounting of the inner container ( 3 ) or the intermediate container ( 3 ) consists of a plurality of spring elements ( 10,111 ) that encompass, side by side, in the longitudinal direction of the jacket ( 5 ) and on all sides thereof, the intermediate container ( 3 ) or the inner container ( 2 ). The spring elements ( 10, 11 ) for their part are provided with shock absorbers.

According to the IAEA Safety Standard Series—Regulations for the SafeTransport of Radioactive Material 1996 Edition Regulations no. TS-R-1(ST-1 Revised) of the International Atomic Energy Agency, Vienna (Germanversion BfS-ET-31/00) July 2000 salt meshes are subjected to extremedegradation in the so-called Type B casks for transporting and storinghighly radioactive materials.

These regulations are revised and set down in detail in English versionST-1. In general there are the following mechanical, thermal, andradiological recommendations:

Nine-meter drop test, pin-drop test, heat test, water-pressure test, aswell as handling regulations and regulations regarding reporting ofaccidents.

According to industry-wide requirements that are based on the world-wideIAEA Regulations and that correspond to the recommendations of theaccident-rectifying regulations (according to GGVS/ADR, GGVS/RID,GGVSee/JMDG) the construction of the Type B shipping elements (these arethe casks with a radioactive inventory above the limit where theirrelease does not create any increased danger) are based on mechanical,thermal, and radiological tests that ensure the safety of the casks evenin severe accidents. They are thus the sole category of safety packagewhere the safety is ensured even in the case of severe accidents.

The mechanical tests for Type B shipping elements, the standard massiveheavy vessels, belongs to the nine-meter drop s sequence onto a rigidfloor and a one-meter drop onto a pin in the position in which the caskis most seriously damaged, which means that for each test there must bea number of drops so that the worst damage for the various parts of thecask can be assessed for each drop. The thermal test following the droptest is a 30-minute burn with complete flame envelopment of the cask byan open fuel-oil flame which heats the entire cask to at least 800° C.These tests set by the IAEA regulations simulate “real” accidentsituations (prior to 11 Sep. 2001) and have quite a margin of safety.

In mechanical tests it is very important that the cask be dropped on anunyielding floor as this rigidity is not really encountered in realaccidents. Since the cask mass is multiplied by the impact decelerationto produce the actual impact force, a nine-meter drop onto a rigid floorproduces an impact force that is much higher than that reached inreality on impacting at a much higher speed on a softer floor. Thisdetermination as well as the fact that in particular Type B cask thatare used for the shipping of spent fuel elements and highly radioactivewaste as a result of their massive construction have much greater safetyin severe accidents as can be determined by a number of tests.

In addition the Type B cask must comply with radiological requirements.These requirements are also spelled out in ST-1.

Furthermore the container system can be used without this ion shieldingfor example for other dangerous materials.

What is more, it is essential to take into account what will happen whentraveling by train, truck, or boat. Even the analysis of accidents mustbe done according to the requirements of the IAEA and country-specificrequirements.

The known so-called Castor casks do not comply in various ways to therequirements of the IAEA and the applicable German requirementsregarding transport and storage.

This type of cask is made by machining as a monolithic object cut from amonolithic block of spherical-graphite cast iron and is provided withseparate bores and with machined cooling ribs and are provided to holdspent fuel elements in water in storage pools (wet storage) in which thefuel elements are maintained cool (at least 5 years).

Thus the complete machined but monolithic and thick-walled cask blocksweighing between 100 and 150 t and holding spent fuel elements arecompletely submerged. The normally brittle surface of the mechanicallymachined anthracite casting must be given some surface treatment.

Here in the contaminated storage-pool water the spherical-graphite blockcask is contaminated inside and outside. As a result it is necessary tometiculously decontaminate the exterior (1998 was the start of acomplete handling ban from outside contamination).

The required IAEA drop tests cannot be done with an empty cask. Theselected spherical-graphite material does not resist such forces createdby mass times acceleration without bursting because of the brittlenature of the material. Trials cannot be made according to the necessaryregulations either by calculation (with a substantial margin for error).The actual results can be calculated with models provided with shockabsorbers and actually done with Pollux and the so-called JapaneseCastor casks.

This testing of the Pollux and Japanese Castor casks, which are providedwith large top and bottom shock absorbers only gives results that relateto the shock absorbers and not to the actual strength of the casks.

This results in the following rule: Castor casks with top and bottomshock absorbers must be integrated into form Type B container systems.

The actual spherical-graphite cask is never actually tested. Even theflame test, with 800° C. for at least 30 minutes, is not done. To datethere is no reliable data.

It is an object of the present invention to provide a container systemof the described type that complies with the above-given requirements ofthe national and international rules and remains undamaged whensubjected to the necessary tests, with no release of radioactivity.

This object is attained according to the invention in that the containersystem comprises an outer vessel and an inner vessel surrounded by theouter vessel and holding the radioactive material.

This structure has the advantage that all potential damaging from theexterior is completely or nearly completely absorbed by the outercontainer so that the inner container is itself not affected or is solittle affected that there is no damage to the inner container. Whensufficiently strong materials are used in spite of any inherentelasticity the outer container can be constructed that even when it isdamaged or even destroyed it still generally acts like a sacrificialcontainment that on its own satisfies the IAEA requirements. Thus thecontainer system can be constructed such that it is used to hold the nolonger compliant Castor casks in that they can be put in an outercontainer according to the invention without head and shock absorbersfor safe transport and storage.

Further details of the invention are in the following detaileddescription and the attached drawings in which a preferred embodiment ofthe invention is shown by way of example. In the drawing:

FIG. 1 is a longitudinal section through a container system with anouter container, an intermediate container, and an inner container;

FIG. 2 is a cross section through the container system along line II-IIof FIG. 1;

FIG. 3 is a longitudinal section through the outer container in explodedview;

FIG. 4 is a longitudinal section through the intermediate container;

FIG. 5 is a longitudinal section through the middle and innercontainers;

FIG. 6 is longitudinal section through the middle and inner containersin exploded view; and

FIG. 7 is a longitudinal section through an outer container inside astandard Castor cask.

A container system according to the invention basically comprises anouter container 1 and an inner container 2 surrounded by an intermediatecontainer 3 inside it.

The outer container 1 comprises a cylinder 4 whose side wall 5 is formedof prestressed reinforced spun concrete. It is further provided with acover 6 and a floor 7 that are made of reinforced concrete, preferablyalso of prestressed spun reinforced concrete with boron oxide foradditional moderating of neutrons that are present in the radioactivematerial inside the inner container 2.

The outer container 1 defines a chamber 8 having an inner surface 9 onwhich are braced springs 10 and 11 also braced on the cover 6 and floor7. These springs 10 and 11 are preferably provided with (unillustrated)shock absorbers, as for example used in the suspensions of rail cars.

The springs 10 braced against the side wall 5 are distributed about thesurfaces 9 to be rotation symmetrical and a plurality of the springs 10are distributed longitudinally of the side wall 5 next to or one abovethe other.

The springs 11 braced on the floor 7 and cover 6 are also uniformlyarrayed on the cover 6 and floor 7. They have longer travel strokes andgreater stiffness than the springs 10 braced against the inner surface 9of the side wall 5.

Each spring 10 and 11 is provided with an (unillustrated) prestressingdevice that prestresses it outward against the outer container 1. Tothis end the prestressing devices can be threaded bolts that extendthrough the side wall 5, the cover 6, and the floor 7 and engage with aninternal thread in a pusher washer against which the respective spring10 and 11 bears toward the inner chamber 8.

The inner container 2 is wholly inside the intermediate container 3 onwhose outer surface 12 and cover 13 and floor 14 bear the springs 9 and10.

Here the side wall 12 of the intermediate container 3 is made ofprestressed spun reinforced concrete. The cover 13 and the floor 14 arealso of reinforced concrete, preferably prestressed spunreinforced-concrete with boron oxide for additional moderating ofneutrons that are emitted by the radioactive materials in the innercontainer 2.

The intermediate container 3 has on an inner wall surface 15 and on theinner surfaces 16 and 17 of its cover 13 and floor 14 layers 18, 19, and20 of polyethylene that moderate neutrons that come from the radioactivematerial in the inner container 2.

The inner container 2 is also a cylinder that is double-walled and ofstainless steel. Between the inner wall 21 and the outer wall 22 of itsside wall 23, its cover 24, and its floor 25 are spaces 26, 27, and 28in which a gamma- and neutron-ray shielding absorber 29 is provided.Thus the absorber 29 completely surrounds an inner chamber 30 such thatno gamma or neutron ray windows are left. The absorber 29 can be formedof depleted uranium (uranium oxide) or a similarly effective material.

The inner container 30 has a particularly smooth surface finish on innersurfaces of the inner walls 21 and on outer surfaces 32 of the outerwalls 22.

The inner container 2 has a surface 33 turned toward the cover 24 andannular flange 34 that projects above the inner container 2 and that isof such an outer diameter that it conforms to the outer surface 35 ofthe intermediate container 3 so that the radial outer surface 36 isflush with the outer surface 35 of the intermediate container.

The inner container 2 has adjacent and inside the annular flange 34 amounting ring 37 that closes an annular gap between the inner wall 21and the outer wall 22 of the inner container 2. The mounting ring 37 isprovided with threaded bores 37 holding mounting bolts 39 that passthrough and secure in place the cover 24 of the inner container 2.

Above the cover 24 of the inner container is an intermediate cover 40that is secured by threaded bolts 41 to the annular flange 34 and thatcovers with its lower face 42 the adjacent polyethylene layer (13).

The side wall 5, the cover 6, and the floor 7 of the outer container 1as well as the side wall 12, the cover 13 and the floor 14 of theintermediate container 3 are traversed by empty tubes 43 and 44 in whichare arranged mounting elements for prestressing and tightly closing theouter container 1 and the intermediate container 3. The mountingelements 45 and 46 are tie rods.

The outer container 1 is provided near its floor 7 with air-inletopenings 47 and near its cover with air-outlet openings 48 that aredistributed radially symmetrically about the side wall 5. The inletopenings 47 and the outlet openings 48 are closable.

Instead of the inner container 2 shown here with the shielding and theintermediate container, the outer container 1 can hold in its innerchamber 8 an industry-standard Castor cask 49 and thereby form amonolithic inner container 50. The Castor ray window is covered in theinterior chamber 8 by layers of polyethylene.

The stainless steel used for the inner container 2 is made particularlysmooth on both the inner wall 21 and the outer wall 22 so that anycontamination can be held as low as possible and so as to facilitatedecontamination as much as possible. The inner wall 21 and the outerwall 22 are thus preferably at most 40 mm thick. The absorber 29 in thecavities 26, 27, and 28 is mainly enriched uranium (uranium dioxide) orsimilar materials that function particularly as gamma- and neutron-rayshield not only because of their mass but because of their properties.

The layers 18, 19, and 29 of polyethylene 18, 19, and 20 have theexclusive task of neutron shielding. Unlike the standard casks herethere is a closed cask. By putting the inner container 2 in theintermediate container 3 there is a further complete shield containerwith a unifying corona effect of prestressed reinforced spun concrete,as very clearly described in DE 199 19 703. The use of prestressedreinforced spun concrete produces an extraordinarily strong and stiffbut light body that even though of lesser weight has better mechanicalproperties than spherical-graphite cast iron. Even the shielding is atleast as good. In addition prestressed reinforced spun concrete has ahighly uniform and smooth surface that does not need to be painted andthat is also decontaminated without great expense.

The inner container 2 and the intermediate container 3 have in generalall the necessary features to constitute a shipping unit according tothe IAEA requirements. In order however to insure that mechanical,thermal, and radiological requirements are met in the required tests(drop test, accident test, burn test), the inner container 2 and theintermediate container 3 are also both made out of prestressedreinforced spun concrete like the outer container 1 that itself isdimensioned such that the inner container 2 and the intermediatecontainer 3 can be fitted inside with room to move.

This is made possible by the prestressed springs 10 and 11 that arebraced in all directions on the intermediate container 3. Theenergy-dissipating travel required by the accurately determined play canbe related proportionally from the travels of the springs 10 and 11 andcan be transformed into (damped) movements.

The springs 10 and 11 distributed rotation symmetrically about the sidewall 5 of the outer container 1 and longitudinally of the outercontainer 1 are prestressed such that the mass of the inner container 2with the intermediate container 3 (about 80 t) when horizontal shiftsonly slightly out of a central position. Even when the outer container 1is vertical the springs 11 at the cover 6 and the floor 7 are set upsuch that there is no significant displacement of the inner container 2.The spring prestressing is in any case so great that the weight of theinner container 2 and the intermediate container 3 do not cause a shift.

The container system according to the invention is used as follows:

Once all the springs 10 and 11 are tensioned by their tensioningelements 10 and 11 such that they are clear of the side wall 12, cover13, and floor 14 of the intermediate container 3, it is raised out ofthe outer container 1. Once the cover 13 of the intermediate container3, the intermediate cover 40, and the cover 24 of the inner container 2have been lifted off, the intermediate container 3 is dropped with theinner container 2 into the decay pool and the connection between theinner container 2 and the intermediate container 3 is released such thatthe inner container 2 can be lifted out of the intermediate container 3and dropped into another intermediate container 3. This has theadvantage that any radioactivity on the first intermediate containerdoes not have to be taken care of, only those regions of the annularflange 34 that are in direct contact in the pool with the radioactivewater. In order to fill another inner container, the first intermediatecontainer 3 is fitted with the inner container 2 and dropped into thepool.

After the inner container 2 and the intermediate container 3 are in thechamber 8 of the outer container 1, the cover 6 is closed. Then thesprings 10 and 11 are set and released by screwing out the tensioningelements and fitting plugs to the holes that they leave. The outercontainer that is thus filled with radioactive material emits noradiation at all to the outside due to the several shieldings.

Since spent fuel elements emit heat for a very long time after theiruse, they pose for a long time a considerable thermal stress to theirenvirons. The result is that the inner container 2 and the intermediatecontainer 3 are at a temperature of 300-500° C.

In order to exploit this energy, the outer container is provided at itsfloor 7 with air-inlet openings 47 and corresponding air-outlet openings48 near its cover 6. In this manner thermal action (convection) producesa cooling effect of the intermediate container 3 and the inner container2 with the passing air being heated so that its heat energy can beexploited after it leaves the outlet openings 48, thereby avoiding theuse of an expensive cooling and ventilating system for the storage areaholding the container system. Calculations indicate that a heat-energyoutput of about 20 kW can be counted on from each container system.

Since the intermediate container 3 and the inner container 2 are mountedmovably in the outer container 1 by the springs 10 and 11, little heatis transmitted across to the walls of the outer container 1. Theair-inlet openings 47 and the air-outlet openings 48 are closable so asfully to closed off the interior 8 of the outer container 1 in the eventof a fire or for a submersion test.

The container system protects against any type of mechanical action fromoutside by the use of the extremely strong materials, the springsuspension, and the mechanical shielding of the radioactive material inthe inner container 2 and intermediate container 3. One or more blowsstruck as a test against the outer container 1 are withstood withoutsubstantial damage in particular as they are only affective against itsown mass while the inner container 2 and intermediate container 3 areset in damped movement in the inner space 8. This is so effective thatthe container system can also survive an aircraft accident unscathed. Itis so strongly made that it withstands a load drop of 1 t at adeceleration of 300 m/s². Even the failure of the floor of a storagefacility, which resembles an aircraft accident, is survived by thecontainer system. Thus it is possible to use them on the insufficientlystable floors in the Gorleben, Ahaus, and Rugenow storage facilities.

The container system is also safe when completely enveloped by fire.According to the IAEA rules a container must be able to withstand atemperature of 800° C. when enveloped by flames for 30 min. The systemaccording to the invention has withstood a temperature of 1000° C. for 3hours (New York rule).

Both the inner container 2 and the intermediate container 3 satisfy allradiological requirements, especially for spent fuel rods. The depleteduranium (uranium oxide) and the like have a shielding capacity such thatthe activity measured outside the inner container 2 is substantiallylower than the minimum required level.

The container system is also optimally designed against the effect ofarmor-piercing projectiles, as encountered in terrorist acts. Anarmor-piercing shot fired against the outer container 1 is completelystopped because of its extreme strength. Even if the armor-piercinground makes a small hole in the outer container and a heated-gashigh-pressure wave created by the hollow charge enters the chamber 8 ofthe outer container 1, this gas will uniformly fill the space 8 and actuniformly from outside on the intermediate container 3 and the annularflange 34 of the inner container 2 without damaging either.

The sudden pressurization be relieved through the inlet and outletopenings 47 and 48.

The already described advantages of the container system can also beused in order so as to employ the no longer compliant Castor casks 49.These must otherwise be retired, which is a huge waste in view of thelarge number already in existence. Here the outer container 1 is madesuch that it can contain an existing Castor cask and can thus employ thealready existing manipulating and storing equipment.

1. A container system for transporting and storing highly radioactivematerials, characterized in that it comprises an outer container (1)holding at least one inner container (2) that itself holds theradioactive material:
 2. The container system according to claim 1,characterized in that the inner container (2) is supported by springs inthe outer container (1).
 3. The container system according to claim 1,characterized in that the outer container is comprised of a cylinder (4)having a side wall (4) of reinforces prestressed spun concrete with forexample boron oxide as an additional neutron absorber.
 4. The containersystem according to claim 3, characterized in that the outer containerhas a cover (6) and a floor (7) that are made of reinforced concretewith the addition of for example boron oxide as an additional neutronabsorber.
 5. The container system according to claim 4 characterized inthat the cover (6) and the floor (7) are made of prestressed reinforcedspun concrete with the addition of for example boron oxide as anadditional neutron absorber.
 6. The container system according claim 5that springs (10 and 11) bear against an inner surface (9) of the sidewall (5), of the cover (6), and of the floor (7).
 7. The containersystem according claim 6, characterized in that the springs (10 and 11)are provided with shock absorbers.
 8. The container system accordingclaim 7, characterized in that the springs (11) bearing on the cover (6)and the floor (7) have a long spring travel and a high spring constant.9. The container system according claim 8, characterized in that thesprings (10) bearing on the side wall (5) have a short spring travel anda low spring constant.
 10. The container system according claim 9,characterized in that springs (10) bearing on the side wall (5) aredistributed rotation symmetrically about its inner surface (9).
 11. Thecontainer system according claim 10, characterized in that a pluralityof the springs (10) are distributed in a row longitudinally of the sidewall (5).
 12. The container system according claim 11, characterized inthat each spring (10 and 11) is provided with a prestressing device thatprestresses it outwardly toward the outer container (1).
 13. Thecontainer system according claim 12, characterized in that theprestressing devices are threaded bolts that extend through the sidewall (5), the cover (6) and the floor (7) and engage with an internalthread in a bracing washer that the springs (10 and 11) bear inward on.14. The container system according claim 13, characterized in that theinner container (2) is generally completely enclosed in an intermediatecontainer (3) having a side wall (12), a cover (13) and a floor (14)against which the springs (10 and 11) are braced.
 15. The containersystem according claim 14, characterized in that the side wall (12) ofthe intermediate container (3) is made of prestressed reinforced spunconcrete with the addition of for example boron oxide as an additionalneutron absorber.
 16. The container system according claim 15characterized in that the cover (13) and the floor (14) of theintermediate container (3) is made of reinforced concrete with theaddition of for example boron oxide as an additional neutron absorber.17. The container system according claim 15 characterized in that thecover (13) and the floor (14) of the intermediate container (3) is madeof prestressed reinforced spun concrete with the addition of for exampleboron oxide as an additional neutron absorber.
 18. The container systemaccording claim 17, side-wall, cover, and floor inner surfaces (15, 16,and 17) of the intermediate container (3) have respective polyethylenelayers (18, 19, and 20) for moderating neutrons generated by theradioactive material inside the inner container (2).
 19. The containersystem according claim 18, characterized in that the inner container (2)is double-walled and has between the inner wall (21) and outer wall (22)of its side wall (23), of its cover (24), and of its floor (25) spaces(26, 27, and 28) a gamma- and neutron-ray absorber (29).
 20. Thecontainer system according claim 19, characterized in that the absorber(29) generally fully surrounds an inner chamber (30) of the innercontainer (2).
 21. The container system according claim 20,characterized in that the absorber is comprised of depleted uranium(uranium oxide) or a similarly effective material.
 22. The containersystem according claim 21, characterized in that the inner container iscomprised of stainless steel with contamination-reducing smoothsurfaces.
 23. The container system according claim 22, characterized inthat the inner container (2) has on an upper surface of its cover (24)an annular flange (24) that projects outward from the inner container(2) and that is of the same outer diameter as an outer surface of theside wall (12) of the intermediate container (3).
 24. The containersystem according claim 23, characterized in that the inner container (2)has a mounting ring (37) closing an annular gap between the inside wall(21) and the outer wall (22) at the annular flange (34) and formed withthreaded bores (38) receiving mounting bolts (39) that traverse andsecure the cover (24) of the inner container (2).
 25. The containersystem according claim 24, characterized in that above the cover (24) ofthe inner container (2) there is an intermediate cover (40) that issecured by threaded bolts (41) to the annular flange (34) and that iscovered on its lower face (42) by a layer of polyethylene (13).
 26. Thecontainer system according claim 25, characterized in that the sidewalls (5 and 12), the covers (6 and 13), and the floors (7 and 14) ofthe outer container (1) and of the intermediate container (3) pareprovided with longitudinally throughgoing tubes (43 and 44) in which areprovided mounting elements (45 and 46) for prestressing and closing theouter container (1) and the intermediate container (3).
 27. Thecontainer system according claim 26, characterized in that the mountingelements (45 and 46) are tie rods.
 28. The container system accordingclaim 27, characterized in that the outer containers (1) is providedadjacent its floor (7) with a plurality of air-inlet openings (47) andnear its cover (6) with a plurality of air-outlet openings (48)distributed radially symmetrically over the side wall (5).
 29. Thecontainer system according claim 28, characterized in that the air-inletopenings (47) and the air-outlet openings (48) are closable.
 30. Thecontainer system according claim 13 and 27 to 29, characterized in thatthe inner container (2) contained in the outer container (1) is astandard Castor cask (49).